McGill grading scale:

A 85+
A- 80-84
B+ 75-79
B 70-74
B- 65-69
C+ 60-64
C 55-59
D 50-54
F 49-

Applied to our exams, which consist of three questions worth 33 points each, this scale yields roughly the following per-question grading scale:

A 28+
A- 26.5-28
B+ 25-26.5
B 23-25
B- 21.5-23
C+
20-21.5
C 18-20
D 16.5-18
F 16.5-